Plant tray structures are widely used in greenhouse and planting operations today. A problem associated with a conventional plant tray is root-tangling or root-binding which deter development of the plant roots after the plants are transplanted. As an example of air-pruning plant growing trays which prevents root-binding, one is referred to the disclosure found U.S. Pat. No. 3,712,252.
One particular important application for plant trays is their use in conjunction with an automatic transplanter such as that disclosed by Dr. Barney K. Huang in U.S. Pat. No. 3,446,164. In such a case, the plant tray includes a series of plant cells that are open about the bottom and top with the plant extending from the top of each individual cell. Because of the particular taper of such a plant tray and because the bottom of the plant tray is open, it has been appreciated that individual plants can be extracted from the bottom of the plant tray and directed into the field by an automatic transplanter. However, one particular problem that has been presented with an open bottom plant tray of the type being discussed; is it is very difficult to confine and hold the plant growing medium, such as peat cake or peat mix, in the plant tray cells, especially during the early phases of the seed germination and root development. Again, it is important from the standpoint of providing air-pruning that the bottom of a plant tray be substantially open. Therefore, there has been and continues to be a need for a plant growing tray that will effectuate air-pruning but will still act to confine and retain the soil growing medium within the tray cells.